Band 20, which represents the 800Mhz, is supported by both. The M1 and M2. I am also a Swisscom customer and live in a rural area. But since I also have B3 (1800 Mhz) and B1 (2100 Mhz) in addition to the B20, the M2 makes more sense with a corresponding subscription (in one premium) with full speed, since it manages carrier aggregation better. With the M1, for example, it was approx. 120Mbit, whereas at the same location the M2 manages up to 220Mbit in a stable manner in the flat.
My personal tip: Use the Netmonster app to test which bands you have and then decide. Band 20 alone technically delivers a maximum of about 50 Mbit. It is also important which subscription you have (Swisscom direct or low-cost providers such as Wingo and Mbudget with a lower network priority) and how busy the antennas are.
Good luck.